Nuclear Stellar Properties of Swift-BAT AGN and Matched Inactive Galaxies

MNRAS 473, 4582–4611 (2018) doi:10.1093/mnras/stx2618 Advance Access publication 2017 October 9

LLAMA: nuclear stellar properties of Swift-BAT AGN and matched inactive galaxies

Ming-Yi Lin,1‹ R. I. Davies,1‹ E. K. S. Hicks,2 L. Burtscher,1 A. Contursi,1 R. Genzel,1 M. Koss,3 D. Lutz,1 W. Maciejewski,4 F. Muller-S¨ anchez,´ 5 G. Orban de Xivry,6 C. Ricci,7 R. Riffel,8 R. A. Riffel,9 D. Rosario,10 M. Schartmann,1,11,12 A. Schnorr-Muller,¨ 8 T. Shimizu,1 A. Sternberg,13 E. Sturm,1 T. Storchi-Bergmann,8 L. Tacconi1 and S. Veilleux14 1Max–Planck–Institut fur¨ extraterrestrische Physik, Postfach 1312, D-85741 Garching, Germany 2Department of Physics and Astronomy, University of Alaska Anchorage, AK 99508-4664, USA 3Institute for Astronomy, Department of Physics, ETH Zurich, Wolfgang–Pauli–Strasse 27, CH-8093 Zurich, Switzerland 4Astrophysics Research Institute, Liverpool John Moores University, IC2 Liverpool Science Park, 146 Brownlow Hill, L3 5RF, UK 5Center for Astrophysics and Space Astronomy, University of Colorado, Boulder, CO 80309-0389, USA 6Space Sciences, Technologies, and Astrophysics Research Institute, UniversitedeLi´ ege,` 4000 Sart Tilman, Belgium 7Instituto de Astrof´ısica, Facultad de F´ısica, Pontiﬁcia Universidad Catolica´ de Chile, Casilla 306, Santiago 22, Chile 8Departamento de Astronomia, Universidade Federal do Rio Grande do Sul, IF, CP 15051, 91501-970 Porto Alegre, RS, Brazil 9Departamento de F´ısica, Centro de Cienciasˆ Naturais e Exatas, Universidade Federal de Santa Maria, 97105-900 Santa Maria, RS, Brazil 10Department of Physics, Durham University, South Road, Durham, DH1 3LE, UK 11Centre for Astrophysics and Supercomputing, Swinburne University of Technology, Hawthorn, Victoria 3122, Australia 12Universitats–Sternwarte¨ Munchen,¨ Scheinerstrasse 1, D-81679 Munchen,¨ Germany 13Raymond and Beverly Sackler School of Physics and Astronomy, Tel Aviv University, Ramat Aviv 69978, Israel 14Department of Astronomy and Joint Space–Science Institute, University of Maryland, College Park, MD 20742-2421, USA

Accepted 2017 October 5. Received 2017 October 5; in original form 2017 June 10

ABSTRACT In a complete sample of local 14–195 keV selected active galactic nuclei (AGNs) and inactive galaxies, matched by their host galaxy properties, we study the spatially resolved stellar kinematics and luminosity distributions at near-infrared wavelengths on scales of 10–150 pc, using SINFONI on the VLT. In this paper, we present the first half of the sample, which comprises 13 galaxies, eight AGNs and five inactive galaxies. The stellar velocity fields show a disc-like rotating pattern, for which the kinematic position angle is in agreement with the photometric position angle obtained from large scale images. For this set of galaxies, the stellar surface brightness of the inactive galaxy sample is generally comparable to the matched sample of AGN, but extends to lower surface brightness. After removal of the bulge contribution, we find a nuclear stellar light excess with an extended nuclear disc structure, which exhibits a size-luminosity relation. While we expect the excess luminosity to be associated with a dynamically cooler young stellar population, we do not typically see a matching drop in dispersion. This may be because these galaxies have pseudo-bulges in which the intrinsic dispersion increases towards the centre. And although the young stars may have an impact in the observed kinematics, their fraction is too small to dominate over the bulge and compensate the increase in dispersion at small radii, so no dispersion drop is seen. Finally, we find no evidence for a difference in the stellar kinematics and nuclear stellar luminosity excess between these active and inactive galaxies. Key words: galaxies: kinematics and dynamics – galaxies: photometry – galaxies: Seyfert – galaxies: spiral.

E-mail: [email protected], [email protected] (M-yL); davies@ mpe.mpg.de (RID)

C 2017 The Authors

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with XSHOOTER. This is the LLAMA (Luminous Local AGN 1 INTRODUCTION with Matched Analogues) survey, which has been the focus of sev- It is widely accepted that most galaxies harbour a supermassive eral other studies (Schnorr-Muller¨ et al. 2016; Davies et al. 2017, black hole (SMBH). The most remarkable BH observations are Rosario et al. submitted, Burtscher et al. in preparation). of the Galactic Centre where the individual stars can be spa- In this paper, we present the SINFONI H+K observations prob- tially resolved and followed through their orbits, accurately con- ing radial scales of ∼150 parsec for the first half of the AGNs straining the SMBH mass (for a review see Genzel, Eisenhauer from Davies et al. (2015) and their corresponding inactive galaxies & Gillessen 2010). Beyond the Milky Way, the most compelling which are matched in stellar mass, morphology, inclination and the evidence is the correlation between the mass of SMBH and stel- presence of a bar. This contains a total of 13 galaxies, eight AGNs lar velocity dispersion of the bulge component of the host galaxy, and five inactive galaxies, which provide eight pairs (since some which is interpreted as the signature of coevolution and regulation inactive galaxies can be well matched to more than one AGN). In between the SMBH and the bulge (see Kormendy & Ho 2013 and this study, because the sample number is small, when comparing the reference therein). The SMBH grows via inflowing gas accre- a difference between active and inactive sample for any physical tion, resulting in active galactic nuclei (AGN), which have been quantity, we directly compare the mean value and standard devia- observed across different cosmic times. The host galaxy growth tion rather than giving a statistical test. In Section 2, we introduce typically follows two plausible modes (Shlosman 2013): (i) galaxy the observations and data reduction of all the galaxies. Section 3 merger: angular momentum dissipation leads the gas infall forming describes the methodology to extract the stellar kinematics and con- compact young stars in the host galaxy (Holtzman et al. 1992; strain the bulge Sersic´ parameters. The nuclear stellar photometry Hopkins et al. 2009), and furthermore efficiently drives some is in Section 4, while the nuclear stellar kinematics is presented in amount of gas to feed the central SMBH. Examples of this in- Section 5. We summarize our conclusions in Section 6. Throughout clude the ultraluminous infrared bright galaxies with disturbed host this paper, we focus the discussion on the overall kinematic and pho- galaxy morphologies, which are usually accompanied by a QSO- tometric properties of the active and inactive samples. A detailed like luminous AGN (Bennert et al. 2008; Veilleux et al. 2009;Teng descriptions of individual objects with special (or extreme) proper- & Veilleux 2010; Ricci et al. 2017). (ii) Secular process of cold ties will be discussed throughout this paper. We assume a standard −1 −1 gas inflow: gas transfers from outer host galaxy to inner circum- cold dark matter (CDM) model with H0 = 73 km s Mpc , nuclear regions through disc and bar instabilities. If a bar drives = 0.73 and M = 0.27. the gas inflow, the associated inner Lindblad resonance (ILR) may terminate the inflowing gas and redistribute it in a disc inside the ILR radius (see Combes 2001 and references therein). However, 2 SAMPLE SELECTION, OBSERVATIONS Haan et al. (2009) studied gravitational torques and concluded that AND DATA REDUCTION such dynamical barriers can be easily overcome by gas flows from other non-axisymmetric structures. The direct observations of in- 2.1 Matched Seyfert and inactive galaxy sample ∼ flows in an ionized or warm molecular gas phase on 100 pc scales The sample is drawn from the LLAMA project, the selection details have been confirmed in nearby Seyferts (e.g. Storchi-Bergmann and the scientific rationale for which have been described in Davies et al. 2007;Muller¨ Sanchez´ et al. 2009; Riffel, Storchi-Bergmann & et al. (2015). We briefly address and discuss the key aspects of our Winge 2013;Daviesetal.2014; Storchi-Bergmann 2014; Schnorr- target strategy below. Muller¨ et al. 2017). The studies above focus on the question of the origin of inflow- (i) Select AGNs from the 58-month Swift-BAT catalogue: ing gas transport (e.g. ex-situ gas). Once the gas accumulates in the The Swift Burst Alert Telescope (BAT) all-sky hard X-ray sur- nuclear regions, we further want to know whether any in situ star vey is a robust tool for selecting an AGN, because it is based on formation occurs. Some observations indicate on-going star forma- observations in the 14–195 keV band. Emission in this band is gen- tion in the nuclear region (Riffel et al. 2009;Esquejetal.2014) while erated close to the SMBH and can penetrate through foreground others point out the galaxies prefer to have post-starburst popula- obscuration. In contrast to optical/near-infrared AGN classification tions (Cid Fernandes et al. 2004; Davies 2007;Sanietal.2012;Lin techniques, hard X-ray surveys suffer little contamination from non- et al. 2016). Hicks et al. (2013) also find no evidence that on-going nuclear emission. However, it is still biased against extremely ob- 25 −2 star formation is happening in the central 100 pc. Observationally, scured Compton-thick sources (NH ≥ 10 cm , Ricci et al. 2015; it is unclear whether nuclear star formation plays a decisive role in Koss et al. 2016) where the hard X-ray photon attenuation is due triggering nuclear activity. While it is understood that AGN flicker to Compton scattering on electrons rather than photoelectric ab- on and off on very rapid time-scales, a recent analysis points to 105 sorption. In order to create a complete, volume-limited sample of yr as one time-scale (Schawinski et al. 2015); longer duty cycles nearby bright hard X-ray selected AGNs, the selection criteria were 7 − 9 of 10 yr corresponding to the lifetime of a typical AGN phase solely (i) 14–195 keV luminosities: log L14 − 195 > 42.5 (using red- are superimposed on top of that (Marconi et al. 2004). This means shift distance), (ii) redshift: z < 0.01 (corresponds to a distance of ◦ that focusing on the circumnuclear regions of galaxies (e.g. Dumas ≤40 Mpc) and (iii) observable from the VLT (δ<15 ). The total et al. 2007; Hicks et al. 2013;Daviesetal.2014), where dynamical sample contains 20 AGNs covering Seyfert 1, Seyfert 2 and in- time-scales are of order 106 yr and star formation time-scales are termediate Seyfert types. Classifications are based on NASA/IPAC 106–108 yr, is an appropriate strategy to study the feeding mech- Extragalactic Database (NED)1, with additional information from anisms of gas flows associated with AGN activity. To address this the presence of near-infrared broad lines or polarized broad line issue comprehensively, Davies et al. (2015) built a near complete emission, as well as the first spectroscopic data from the LLAMA volume limited sample of 20 nearby active galaxies, which was survey itself. complemented by a matched sample of inactive galaxies, with the aim to obtain high spatial resolution near-infrared observations with SINFONI together with high spectral resolution observations taken 1 https://ned.ipac.caltech.edu/

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Table 1. Galaxy Properties: (1) Pair ID (a – AGN, i – inactive galaxy); (2) galaxy name; (3) AGN classiﬁcation; (4) Hubble type of host galaxy; (5) Presence of large-scale bar (B indicates a bar, AB a weak bar); (6) Stellar mass estimated from total 2MASS H-band luminosity; (7) mK(nucleus), apparent K-band magnitude measured from SINFONI data cube within 3 arcsec aperture size; (8) Large scale axis ratio (from NED or Koss et al. 2011); (9) Inclination derived from axis ratio; (10) Distance (the median value of redshift-independent distance measurements from NED); (11) Physical scale of 1 arcsec (from NED);and (12) Observed 14–195 keV luminosity (70 months average) from Swift-BAT catalogue (Baumgartner et al. 2013).

(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) Pair ID Galaxy name AGN Hubble type Bar M∗ mK a/b Incl. Distance scale log(L14 − 195keV) (M) (mag) (◦) (Mpc) (pc/arcsec) (erg s−1)

1a ESO 137-34 Sey 2 S0/a AB 10.4 11.9 0.79 40 33 185 42.62a 6a NGC 3783 Sey 1.2 Sab B 10.2 10.2 0.89 27 48 212 43.49 7a NGC 4593 Sey 1 Sb B 10.5 11.1 0.74 42 32 200 43.16 4a NGC 5728 Sey 2 Sb B 10.5 11.6 0.57 55 30 199 43.21a 8a NGC 6814 Sey 1.5 Sbc AB 10.3 11.0 0.93 22 23 89 42.69 3a NGC 7172 Sey 2 Sa – 10.4 10.1 0.56 60 34 153 43.45 2a NGC 7213 Sey 1 Sa – 10.6 10.2 0.90 26 22 102 42.50 5a NGC 7582 Sey 2 Sab B 10.3 9.7 0.42 65 22 88 42.67a 6i NGC 718 – Sa AB 9.8 11.2 0.87 30 22 96 – 7i NGC 3351 – Sb B 10.0 11.6 0.93 22 10 74 – 3i, 5i NGC 4224 – Sa – 10.4 11.8 0.35 70 45 193 – 8i NGC 4254 – Sc – 10.2 12.0 0.87 30 16 75 – 1i, 2i, 4i NGC 7727 – Sa AB 10.4 10.8 0.74 42 27 100 —

a 24 −2 Note. Heavily obscured AGNs with NH(column density of neutral hydrogen) ≥10 cm , which is based on C. Ricci et al. (2017, in preparation) modelling 0.3–150 keV spectrum.

(ii) Finding a matched sample of inactive galaxies: 2.2 Observations and standard data reduction Studying the difference between Seyferts and inactive galaxies We present the first part of near-infrared integral field unit (IFU) can provide a direct comparison and give clues to understand what data for the LLAMA project. Eight AGNs and five matched inac- mechanisms can fuel a central BH and how the gas flows (inflows tive galaxies have been observed with SINFONI between 2014 April or outflows) interact with the interstellar medium. However, it is and 2015 June from programme 093.B-0057. In total, this provides important that the inactive galaxies are well matched. To achieve eight Seyfert-inactive galaxy pairs because, by relaxing slightly the this, the inactive galaxies in LLAMA are selected as specific pairs matching criteria, some inactive galaxies provide a good match to to the AGN. The criteria to select an inactive galaxy for each AGN several AGNs. Specifically, NGC 7727 and NGC 4224 are the inac- are based on: host galaxy morphology (Hubble type), inclination tive pair of three and two AGNs, respectively. SINFONI, installed (axisratio)andTwoMicronAllSkySurvey(2MASS)H-band at the Cassegrain focus of VLT-UT4, consists of the Spectrometer luminosity (the proxy of stellar mass). Fig. 3 in Davies et al. (2015) for Infrared Faint Field Imaging (SPIFFI), a NIR cryogenic integral shows that there is no significant difference in the distribution of field spectrometer with a HAWAII 2RG (2k × 2k) detector and an host galaxy properties between the Swift-BAT AGN sample and the adaptive optics (AO) module, Multi-Application Curvature Adap- matched inactive sample, except the distance distribution, the active tive Optics (MACAO Eisenhauer et al. 2003; Bonnet et al. 2004). galaxies being slightly more distant than the inactive pairs. We also We observe each galaxy with the H+K grating at a spectral note that the presence of large scale bar is matched if possible, resolution of R ∼ 1500 for each 0.05 arcsec × 0.1 arcsec spa- but is not strictly necessary. A large scale bar in the host galaxy is tial pixel, leading to a total field of view (FOV) on the sky of an efficient way to drive some gas into the central region (Buta & 3arcsec× 3 arcsec. All scientific objects were observed in the AO Combes 1996). However, numerous studies have found that the bar mode, either using a natural guide star (NGS) or an artificial sodium fraction in Seyfert and inactive galaxies is similar, suggesting that laser guide star (LGS). For our observations to achieve the best cor- while large scale bars may assist in fuelling SMBH growth they rection with an NGS, it should be brighter than R ∼ 15 mag and are unlikely to be the sole mechanism regulating it (Mulchaey & within a distance of 10 arcsec from the scientific object. During such Regan 1997; Cisternas et al. 2015). Our total sample contains 19 observations, the typical Strehl ratio achieved was ∼20 per cent. A matched inactive galaxies. standard near-infrared nodding technique with an observation se- quence of Object-Sky-Object was applied. In each observing block This project includes observations from the high resolution (OB), a total of three sky and six on-source exposures of 300 s each spectrograph XSHOOTER covering 0.3–2.3μm (Schnorr-Muller¨ were obtained, the on-source frames being dithered by 0.3 arcsec et al. 2016, and Burtscher et al. in preparation) and adaptive optics and the sky frames offset by 60 arcsec–100 arcsec. Data from sev- near-infrared integral field spectroscopy covering 1.8–2.4μm taken eral OBs were combined to make the data cube. Telluric stars were with SINFONI (this paper and Lin et al. in preparation). The two observed at similar airmass, either before or after each observing independent sets of observations and analyses allow us to approach, block to make sure they sample similar atmospheric conditions. The from two different perspectives, one of the primary science goals of data were reduced using the SINFONI custom reduction package the overall project: looking for evidence of young or recent stellar SPRED (Abuter et al. 2006), which includes the typical reduction populations (stellar age of a few to a few hundred Myr) related to steps used for near-infrared spectra with the additional routines to AGN accretion. The properties of the sample galaxies analysed in reconstruct the data cube. The standard reduction procedure com- this paper are listed in Table 1. prises flat fielding, identifying bad/hot pixels, finding slit position,

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correcting optical distortion and wavelength calibration. The night- Combing equations (1) and (4) allows one to find the wavelength sky OH airglow emission has been removed by using the methods dependent differential refraction at constant ζ described by Davies (2007). The telluric and flux calibrations for R = 206 265 × (nT,P,f(λ)) × tan ζ (5) the scientific data were carried out with the B-type stars. In our observing strategy, there are at least two data sets for each standard In most cases, the observed shift of the image with wavelength star. We apply the same data processing procedure to standard star was reasonably well approximated by this analytical expression, observations and use these to make a single flux calibration to each although there were a few cases where the match was not so good. science data set. The final flux calibration for both the H band and Fig. 2 in Menezes et al. (2015) shows some examples in which there K band is accurate to ±0.05 mag. are additional offsets that cannot be interpreted as DAR. For example, foreground obscurations (dust filaments or dust lanes cross- ing the nuclear regions) can cause the peak in the H-band image 2.3 Differential atmospheric refraction slightly deviated from the nucleus position of the K-band image To improve the image quality in SINFONI data cubes, we quantify (Mezcua et al. 2016). In order to keep this intrinsic measurement, the displacements induced by differential atmospheric refraction in this work, we correct only the displacements induced by DAR, (DAR), which appears as a spatial offset of the observed object the residual offset is typically small, the average offset in K band as a function of wavelength. The refraction is due to the Earth’s being only ∼0.5 pixels relative to the H band. atmosphere causing the light to deviate from its original trajectory and appears closer to the zenith by an amount that is dependent on 3 ANALYSIS METHODS wavelength. The DAR will be more important for observations with larger zenith distance, i.e. higher air mass. In principle, the DAR 3.1 Stellar distribution and kinematics effect is stronger in the optical and, for seeing limited observations, can usually be ignored in the near-infrared. However, with adaptive In all 13 galaxies, the first two CO absorption bandheads are well optics on large telescopes, the impact of DAR relative to the spa- detected. The stellar kinematics are extracted by fitting the first tial resolution is more significant. We correct DAR using standard of these, the CO(2-0) absorption at 2.2935μm, which has a better analytical expressions based on a simple model of the atmosphere. signal-to-noise ratio (S/N) and less contamination by other absorp- And we include a description here of our method because it differs tion and emission lines. The second CO(3-1) absorption bandhead from the empirical method outlined by Menezes et al. (2015). at 2.3227μm is excluded from the fit since it is contaminated by the An object at an actual zenith distance of z, has an apparent zenith coronal line [Ca VIII] 2.3213μm in AGN. In order to ensure that the distance ζ after the light has passed through the atmosphere. The active and inactive galaxies have a consistent analysis, we fit the refraction angle is R = z − ζ , and can be written as kinematics using only the CO(2-0) bandhead. To improve the S/N of the K-band continuum to 50, and simultaneously preserve the R = 206 265 × (n − 1) × tan ζ (1) 2D kinematics, we have smoothed each slice of the IFU data cube. where R is in arcsec and n is the refraction index close to the Earth’s This is done by convolving with a point spread function (PSF) that surface. has a FWHM of 3 pixels, matching that achieved on the brightest Assuming standard atmospheric conditions, a temperature Seyfert nucleus of NGC 3783 in the same run. To fit each galaxy ◦ 5 T = 20 C, an atmospheric pressure P = 10 Pa and CO2 frac- spectrum in the resulting data cubes, we use the direct pixel fit- n tion of 0.0004 with low humidity, the refraction index 20,105 is ting code Penalized Pixel-Fitting (PPXF) developed by Cappellari & expressed as a function of wavelength (Bonsch¨ & Potulski 1998; Emsellem (2004). We choose the GNIRS sample of Gemini NIR Filippenko 1982) late-type stellar library (Winge, Riffel & Storchi-Bergmann 2009), 2333 983 15 518 which contains 30 stars with stellar type ranging from F7III to n λ − × 8 = . + + −1 ( 20,105 ( ) 1) 10 8091 37 M2III and spectral resolution of 3.4 Å (σ ∼19 km s ). To have the 130 − ( 1 )2 38.9 − ( 1 )2 λ λ same spectral resolution between the stellar library and SINFONI, (2) the stellar templates have been convolved with the instrument’s − where λ is wavelength in μm. To take into account the variation line spread function of 70 km s 1, which is measured from the OH of T and P between the various observations, the refraction index sky lines in Kband. To obtain the line-of-sight velocity distribution nT, P(λ) can be written as (LOSVD) of each galaxy spectrum, the stellar templates are shifted to the systematic velocity and convolved with a Gaussian broaden- n λ − = n λ − ( T,P( ) 1) ( 105,20( ) 1) ing function. A polynomial function of fourth order is added to take into account the power-law continuum from AGN. Unlike the stel- P × [1 + (0.5953 − 0.009 876 × T ) × 108 × P ] lar absorption in the optical wavelengths which often have a higher × (3) S/N ≥ 50 (e.g. Ca II triplet lines measured by Riffel et al. 2015), 93 214.6 × (1 + 0.003 661 × T ) the CO(2-0) absorption in the near-infrared has lower S/N of ∼10 If including the vapour pressure of water, the equation above is per spatial element. We thus do not fit higher-order moments of the reduced by a factor of f Gauss–Hermite series, the h3 and h4 terms, which indicate asym- . metric deviation and peakiness of the profile, respectively (van der 0 0384 −10 nT,P,f(λ) = nT,P(λ) − f × 3.8020 − × 10 (4) λ2 Marel & Franx 1993; Bender, Saglia & Gerhard 1994). Examples of fits and the smoothed stellar templates are shown in Fig. 1.We where f is measured in Pa (the empirical relation between the change apply this fitting procedure to the whole sample across the whole of refractive index and water vapour pressure refer to fig. 4 of FOV to extract the 2D kinematics. The results will be discussed in Bonsch¨ & Potulski 1998): Section 5. 5132 The resulting maps showing the flux distribution of the stellar f = exp 20.386 − × 133.32 273 + T continuum, CO(2-0) equivalent width (EW), stellar velocity and

changing the initial guess of each model component, we find that the choice of initial guesses does not influence the final result significantly. We also note that while the GALFIT output provides a formal χ 2 showing the difference between model and data, this is a purely quantitative assessment and does not fully reflect whether a fit is good. It is more important to judge the quality of the fit from the residual maps. There are two steps in our fitting procedure and are given below. (1) Fitting the large scale disc and bar: we keep the number of the free parameters to a minimum by fixing the Sersic´ index ndisc = 1 and leaving the effective radius r e;disc as a free parameter. In addition, if a large scale bar has been identified in the host galaxy, we fit it using an additional Sersic´ profile. Initially, we allow nbar and r e;bar to be varied; however, if the GALFIT output value for nbar is too small (i.e. nbar ≤ 0.1) or is too similar to the disc (i.e. nbar ∼ 1), we then fix nbar = 0.5, which remains a fairly constant value across 10 Figure 1. The CO absorption features of one active and one inactive different Hubble type within a limited range of M around ∼10 galaxy observed with SINFONI/VLT (top two spectra), and stellar templates M (Weinzirletal.2009). from GNIRS/Gemini convolved to the resolution of SINFONI (bottom two (2) Fitting the large scale bulge: there is no constraint on n spectra). Each spectrum has been corrected for systematic velocity and is bulge and r when we fit the bulge component. The PA and ellipticity shown at rest-frame wavelength. The top spectrum is the sum within the e; bulge AGN-dominated region, and the non-thermal continuum has been removed are set to be in a reasonable range of quantitative agreement with by a polynomial function. The coronal line [Ca VIII] 2.3213µm is blended the observed image. For the active sample, we also include a cen- with CO(3-1) 2.3227µm. The red solid lines for ESO 137-34 (AGN) and tral point source to account for the AGN and avoid nbulge growing NGC 7727 (inactive galaxy) are the example PPXF kinematic fits of the unrealistically large. Note that any structures inside the bulge – for CO(2-0) absorption. example a nuclear disc, circumnuclear ring or nuclear bar – are not considered during the fitting, since they could be a part of the young stellar velocity dispersion are shown for the AGNs and inactive stellar population which we expect to find. galaxies in Figs. 2–3 and Fig. 4, respectively. Studies with large samples of galaxies show that the bulge-to- total luminosity ratio (B/T) increases from late-type galaxies to early-type galaxies, i.e. as a function of Hubble type (Weinzirl 3.2 Continuum luminosity profile et al. 2009). The results of our fitting show a similar trend in our The goal of this study is searching for any nuclear excess stellar small sample as presented in Fig. 5 confirming that the fits are flux, which could indicate a young stellar population and may be reasonable. We also note that there is no difference in B/T between associated with a stellar velocity dispersion drop. The nuclear excess AGN and inactive galaxies, consistent with our selection strategy stellar flux in this paper is defined as additional light in the innermost of matching the active galaxies to the AGN based on host galaxy regions that does not follow the bulge Sersic´ profile. Our FOV is morphology and stellar mass. We find NGC 7213 deviates from only 3 arcsec which, for the nearby galaxies in our sample, is well the relation between the B/T and Hubble type. Its bulge parameter within the galactic bulge. Thus an important step is to understand coupling problem has been discussed and tested in Section 4.4 of the larger scale bulge contribution in which these data reside. Once Weinzirl et al. (2009). Given the Sa morphology, a B/T of ∼0.3 the bulge Sersic´ profile has been derived, then we can check whether only occurs when we fix nbulge = 1, which cannot be distinguished all the nuclear stellar flux follows the larger-scale bulge light profile. from the outer disc, thus we decide to adopt the solution of nbulge = To constrain the bulge Sersic´ profile properly and system- 2.57 with r e; bulge = 13.7 arcsec. The details of the Sersic´ parameters atically, we use the 2D profile fitting algorithm GALFIT (Peng for the bulge, bar and disc are listed in Appendix A. Most galaxies et al. 2002, 2010) to decompose bulge and disc on scales of 2 arcsec– in our sample tend to have small nbulge ∼ 1–2.5, which is likely to 100 arcsec with 2MASS Ks-band data, which trace the stellar light be a discy bulge (pseudo-bulge) instead of a classical bulge with with less bias to extinction or stellar age than optical data. GALFIT n = 4. requires the sky background and a PSF image. The sky background The next step is to match the flux scaling between the 2MASS is set as a fixed parameter and obtained by measuring the mean profile fit and the SINFONI data. In order to compare the radial value in the blank field of the same image. The PSF, which allows gradient between the observation scales, we extract the 1D flux pro- us to correct the seeing, is generated as a Gaussian with FWHM of file along the major-axis direction both from the 2MASS Ks-band 2.5 arcsec. This provided a better residual map than when we used image and the SINFONI stellar continuum image. The stellar con- a bright star obtained from the 2MASS image. Since 2MASS does tinuum is measured from the CO(2-0) absorption bandhead after not provide a pixel noise map, we do not include it in the calcu- correcting the non-stellar AGN contribution2 (Davies et al. 2007; lation. Ordered lists of pixel coordinates have been used as a bad Burtscher et al. 2015). The major-axis PA is the mean value mea- pixel mask, if needed to block bright stars close to the galaxy. For sured from Spitzer near-infrared photometry (Sheth et al. 2010)and each galaxy, we iteratively fit two Sersic´ profiles: one with a vari- able index; and one with the index fixed to an exponential profile. These components aim to model the large scale bulge and the disc, 2 The non-stellar AGN light is estimated from the EW of dilution respectively. Initial parameters are estimated by visual inspection, CO(2-0) bandhead with a given intrinsic EW, which is expected to be a e.g. position angle (PA), ellipticity and effective radius, etc. How- constant value over a wide range of star formation histories and ages [i.e. ever, we note that the best-fitting value derived in the literatures also LAGN = Lobs × fagn,wherefagn = 1 − (EWobs, diluted/EWintrinsic)]. Note that can be regarded as an initial guess for each parameter. By slightly fagn close to 1 corresponds to ∼100 per cent AGN contribution.

Figure 2. Active galaxy sample. Maps are labelled from left to right: stellar continuum ﬂux, CO(2-0) equivalent width (EW), stellar velocity and stellar velocity dispersion. The stellar continuum ﬂux has been corrected for the contribution from non-stellar emission. In CO EW map, the central vacant hole is the region dominated by non-stellar emission that the PPXF program returns a unreliable kinematic measurement. We truncate it for display purposes. Because there is no non-stellar continuum dilution on stellar features for ESO 137-34 and NGC 5728, we do not outline any vacant hole in the centre. In all maps, north is up and east is to the left, the coordinate offset has been converted into the physical scale in parsec.

SINFONI stellar kinematics. Once the bulge Sersic´ index and ef- for WFC3) and higher spatial resolution that better resolves the fective radius have been obtained from the GALFIT decomposition, circumnuclear structures, and these can induce a slight inconsis- and assuming the SINFONI outer region ∼1.0 arcsec–2.0 arcsec is tency in the radial gradient between HST and 2MASS. We care- bulge dominated, we extrapolate the bulge 1D flux profile to a ra- fully minimize this effect due to fine structures when matching the dius <1.5 arcsec and look directly at the residual, to check whether profiles by extending the normalized region to include the large the central few parsecs follow the outer bulge Sersic´ profile. If scale disc. Near-infrared wavelengths are less sensitive to extinc- there is an HST F160W archive image on scales of 0.2 arcsec– tion than the optical (the V band to Ks band extinction ratio is 15 arcsec, we use it to reinforce the connection between SINFONI 1:0.062, Nishiyama et al. 2008), thus we did not correct for any and 2MASS. However, the Hubble Space Telescope (HST)datahave near-infrared extinction in this study. The results are presented smaller pixel scales (0.075 arcsec for NICMOS and 0.038 arcsec in Section 4.

Figure 3. continued. The extreme irregularity in stellar continuum for NGC 7172 and NGC 7582 is due to the asymmetric reddening induced by dust lane, which passes through their nuclear region. The dust lane extinction does not inﬂuence the kinematic measurement. Although NGC 6814 is a face-on system, the weak rotation still is apparent from the map, consistent with the stellar velocity map of Davies et al. (2014).

4 NUCLEAR STELLAR CONTINUUM EXCESS from VLT–SINFONI. An observational caveat is that there are three AGNs (NGC 3783, NGC 4593 and NGC 7172) with strong non- In these sections, we present the 1D radial stellar continuum profile stellar continuum contribution in the centre; therefore it is diffi- for our objects in order to assess whether there is any photometric cult to extract the stellar surface brightness at radii below 50 pc. difference between the AGN and the matched inactive galaxy sam- Obviously, there are two inactive galaxies, which have lower stel- ple. We address this issue from two perspectives: the stellar surface lar surface brightness: NGC 3351 and NGC 4254. The reason is luminosity distribution and the central excess light. that they have about 10 times lower K-band luminosity within our SINFONI field and two times closer distance resulting in ∼1.5 dex lower surface brightness than other galaxies. Except for these two 4.1 Radial distribution of stellar luminosity outliers, the surface brightness for other galaxies which obtained − − Fig. 6 shows the stellar surface brightness of AGNs and inactive with SINFONI H+K grating are about 103 4 L pc 2 and the galaxies, drawn as red and blue lines, respectively. The top left radial surface brightness distributions are generally similar for both panel of Fig. 6 is the directly observed stellar surface brightness active and inactive samples (refer to the bottom left panel of Fig. 6).

Figure 4. Matched inactive galaxy sample. Maps are labelled from left to right: stellar continuum ﬂux, CO(2-0) EW, stellar velocity and stellar velocity dispersion. There is no non-stellar continuum to dilute stellar absorption features, thus the kinematics can be simply extracted. NGC 4254 has no clear velocity gradient because the system is very close to face-on. In all maps, north is up and east is to the left, the coordinate offset has been converted into the physical scale in parsec.

A comparison of the stellar surface brightness between AGNs and matched inactive galaxies has been presented in Fig. 15 in Hicks et al. (2013). They showed that at radii greater than 150 pc, the Seyferts in their sample had a lower surface brightness than the inactive galaxies. However, the luminosity profile was steeper for the AGN, which led to similar, or in some cases higher, surface brightnesses at small radii. The reason leading to the differing results of our LLAMA sample and Hicks et al. (2013) will be discussed together with kinematic comparison in Section 5.3. In addition, we are aware that it is difficult to compare our work directly to the previous Hicks et al. (2013) study because the spatial pixel scales are different. Unlike Hicks et al. (2013) where observations cover a radial range of 50–250 pc, most of our observations cover a smaller range of 10–150 pc. Thus we compare our work to recent Keck OSIRIS data (Hicks et al. in preparation) of a similarly matched sample at spatial scale comparable to VLT–SINFONI. The Figure 5. Individual bulge-to-total luminosity ratio (B/T) as a function of preliminary results have been presented in the right-hand panels of Hubble type. With and without bar component in the 2D decomposition Fig. 6, where the AGN sample is plotted in red while the matched fitting is shown in blue and green colour labelled both in lines and symbols. inactive sample is plotted in blue. NGC 6814 (AGN) has similar sur- The filled circles represent Seyfert galaxies, while the open circles are face brightness in both observations, which is highlighted in green. inactive galaxies. The lines are the mean and standard deviation of B/T as a Based on the data currently available, our small sample shows that function of Hubble type from Weinzirl et al. (2009).

Figure 6. The radial stellar light distribution. Top left panel: the stellar surface brightness as a function of radius for LLAMA sample. All of them were observed with VLT–SINFONI. Top Right panel: the stellar surface brightness as a function of radius for three AGNs and three inactive galaxies, where they were observed with Keck-OSIRIS. AGNs and inactive galaxies are labelled as red and blue lines, respectively. Both observations have covered NGC 6814 (AGN), which we highlight as green colour. Bottom panels: the mean value at that radius and the radial bin size, the error bars are the standard deviationof measurements within each radial bin. The mean value of AGN and inactive galaxy sample are illustrated as bold red and blue lines. The light blue colour isthe mean of all inactive galaxies, while the dark blue colour is the mean of inactive galaxies except for these two outliers (NGC 3351 and NGC 4254).

Table 2. Nuclear properties of each galaxy: (1) Galaxy name, upper rows are AGNs and lower rows are inactive galaxies; (2) Systematic velocity derived from stellar kinematics; (3) Kinematic position angle from stellar velocity ﬁeld; (4) Mean velocity dispersion of bulge (σ at a radius > Rexcess); (5) The trend of velocity dispersion at a radius < Rexcess; (6) Stellar luminosity from SINFONI data cube within approximately 3 arcsec aperture size (depend on how far of good pixels we can achieve); (7) Stellar luminosity of nuclear excess light; (8) L; (9) Size of the nuclear excess light with† (without taking into account the PSF of 0.1 arcsec radius).

(1) (2) (3) (4) (5) (6) (7) (8) (9) Galaxy name vsys PAkin σσtrend log(LK) log(Lexcess) L Rexcess (kms−1)(◦)(kms−1)(L)(L) ( per cent) (arcsec)

ESO 137-34 2791.11 37 105 ± 5 flat 8.19 6.47 1.94 0.40 NGC 3783a 3044.28 137 154 ± 4 drop 8.73 7.95 16.67 0.80 NGC 4593 2553.97 106 149 ± 3 increase 8.15 – – – NGC 5728 2834.28 12 164 ± 4 flat 8.29 7.34 12.15 1.05 NGC 6814 1612.63 37 115 ± 2 flat 8.10 6.11 1.00 0.20 NGC 7172 2591.40 93 103 ± 4 drop 8.52 7.13 4.32 0.60 NGC 7213 1876.60 31 201 ± 3 flat 8.52 7.52 11.00 1.40 NGC 7582 1651.05 155 68 ± 4 flat 8.79 – – – NGC 718 1775.06 13 100 ± 2 flat 8.3 7.04 6.03 0.59 NGC 3351 867.93 174 84 ± 2 drop 7.57 6.95 [6.10]b 32.11[4.52] 2 [0.38]b NGC 4224 2651.79 56 153 ± 2 increase 8.76 7.58 6.95 0.91 NGC 4254 2514.77 87 92 ± 2 increase 7.53 6.57 11.55 0.60 NGC 7727 1885.17 50 187 ± 3 flat 8.53 7.42 8.40 0.70 †We assume the nuclear excess light followed the Gaussian profile, the radius encloses 99 per cent of Gaussian profile. aStrong non-stellar continuum do exist across whole SINFONI FOV that nuclear stellar excess does not take into account in our analysis. bThe luminosity and radius of excess component in the central cusp.

inactive galaxies cover a wider range of surface brightness in ra- Note that this 1D flux extraction method of the central profile has dial range of 10–150 pc, although this tentative conclusion is due to the advantage that it is less susceptible to the stellar light asymmetry the two inactive galaxies that are at least one dex lower in surface induced by foreground dust lane extinction, which can often create brightness than the rest of the sample. We note that some inactive a large discrepancy along the minor axis. Galaxies with a central galaxies have stellar surface brightness comparable to that of AGNs, stellar light deficit then have L < 0, while those with excess have which may suggest that the time-scale of AGN switching on and off L > 0. is shorter than the time-scale to form nuclear stars, and the nucleus Within our sample, most galaxies have a central stellar light of those inactive galaxies may be just in a quiescent phase. Neither excess ranging between 1–12 per cent. Regarding NGC 6814, the data set shows any AGN with stellar surface brightness below 103 central excess is small in physical size. However, we still consider L pc−2 within the central 50 pc, implying the mechanism to trig- this source to be a robust central excess detection. While the size ger AGN happens more effectively in galaxies which have higher is 0.2 arcsec in radius, it is still more than double the typical PSF stellar surface brightness. These conclusions will be revisited once FWHM of 0.1 arcsec. Further, the inner radial slope correspond- the full sample is available. ing to the excess differs from the slope in the outermost regions (0.4–2 arcsec). The L looks small (1 per cent for NGC 6814) because it is measured as the ratio of the additional luminosity to the 4.2 Central excess of stellar light total K-band luminosity within a 3 arcsec aperture. We use this large In this section we look at whether there is an excess or deficit aperture size because it can be easily compared to other public cata- in the stellar continuum compared to the bulge contribution that logues, e.g. 2MASS. On the other hand, if we used a small aperture, was extrapolated from the fit at larger scales. In Section 3.2, we which is matched to the size of the nuclear excess component in described the method we used to measure the Sersic´ index and each galaxy [refer to column (9) in Table 2], we would find the effective radius of the bulge component from large scale 2MASS numbers in the range of 10–50 per cent, rather than 1–12 per cent. Ks-band data. By inward extrapolation of the fitted bulge Sersic´ pro- Thus, even though the L is small, the central excess is still signif- file to the SINFONI FOV, we find that the stellar light at < 1arcsec icant. But notably there are two AGNs which have a central stellar does not always follow the bulge profile. We classify the central light deficit: NGC 4593 and NGC 7582. In order to confirm these stellar light profile as an excess (i.e. cusp) or deficit (see middle light deficit features, we plot the HST/NICMOS/F160W radial flux left panel in Appendix B). A similar dichotomy has been found in along the major axis and find that it matches well with our SINFONI early-type galaxies in Virgo and Fornax clusters (Cotˆ eetal.´ 2007). radial flux profile. The deficit could be due to either the intrinsic Although our study focuses on Seyferts and inactive galaxies, many central behaviour or to the foreground dust extinction. NGC 7582 of which are late-type, we adopt a similar concept to parametrize is an example of the latter case, where the foreground dust lane the inner stellar profile. We introduce a parameter, L, as a ratio across the circumnuclear region causes the stellar light asymmetry. of the observed discrepancy in the SINFONI K-band luminosity However we cannot rule out that its stellar light deficit is intrinsic. (i.e. the difference between the stellar luminosity and the extrapo- The central stellar light deficit in NGC 4593 is likely to be intrinsic lated bulge contribution) to the total SINFONI K-band luminosity and is unambiguously observed in both SINFONI and NICMOS in a 3 arcsec aperture. This is estimated from the 1D flux profile radial flux profiles. Furthermore, we try to measure the bulge Sersic´ extracted along the major-axis PA and then, assuming their radial profile solely based on HST/NICMOS/F160W image for these two distribution is symmetric, L is a radial integration until the radius galaxies by using GALFIT algorithm. NGC 7582 has strong asymmet- where there is no significant excess light (i.e. Rexcess in Table 2). ric photometry, so that we cannot constrain the bulge Sersic´ profile

(NSC). Boker¨ et al. (2004) investigated the nearby late-type face-on spiral galaxies and found the optical i-band luminosity of NSCs (mean ∼106.4 L) strongly correlates to its host galaxy luminosity, but the size-luminosity correlation of NSCs is weak. On the other hand, Cotˆ e´ et al. (2006) studied the compact central nuclei of early- type galaxies in the Virgo cluster in both g-band and z-band images and found that the size-luminosity relation of NSCs is r ∝ L0.5,where the mean luminosity of an NSC is ∼107.7 L. Such a relation can be understood in terms of a merger model: the radius of the nucleus increases with increasing total luminosity as globular clusters merge (Antonini 2013). In our sample, the mean K-band luminosity for nuclear excess stellar light is ∼107 L, which is comparable to those NSCs found in the nuclei of early-type or late-type galaxies, 7 if we assume NSCs mass of ∼10 L with M/LH of 0.6 (Seth et al. 2010; Antonini 2013). However the size of the excess nuclear Figure 7. The size-luminosity relation of excess nuclear star light (i.e. stellar light in our study is not matched to those of NSCs. The excluding the objects with central deficit star light). The excess star light is typical size of NSCs is 5 pc, although a few of them can extend to defined as a region, where the radial stellar light distribution does not follow 20–30 pc. In contrast, for our sample, we find a mean size of ∼80 pc, the prediction of outer fitted bulge Sersic´ profile. The filled circles represent and the size of individual nuclei ranges from 200 pc down to 10 pc. Seyfert galaxies, while the open circles are inactive galaxies. Circle with These are more likely to be an extended nuclear stellar disc rather different colour is given for each object. NGC 3351 has two measurements, than NSCs (Balcells, Graham & Peletier 2007). The reason that the open square is the entire excess star light within the entire SINFONI FOV, we cannot observe NSCs is due to the distance of our sample and while the open circle is an excess cusp appearing in the innermost region. Since the strong non-stellar dilution surrounds entire SINFONI FOV in NGC the corresponding physical pixel scale is at least 10 pc, thus the 3783, it has been excluded in this plot. NSCs cannot be spatially resolved. The extended size of the nuclear discs gives clues, that such objects might have a different nature properly. On the other hand, for NGC 4593, although the radial and structure than either compact NSCs or the bulge. The size- Sersic´ profile of bulge component is shallower (i.e. the amount of luminosity relation of the nuclear discs suggests their formation deficit light decreases), we still do not find any significant stellar may nevertheless have some similarities to that of NSCs, in terms excess towards the centre; the detailed results are presented in the of the merging of sub-units. top right panel of Fig. B7. For galaxies with central stellar light excess, we fit a Gaus- 5 NUCLEAR STELLAR KINEMATICS sian function to characterize the size of the excess component (a similar method has been used in dwarf elliptical galaxies by In terms of stellar kinematics, the inactive galaxy sample is rela- Graham & Guzman´ 2003). The radius encloses 99 per cent of the tively simple to analyse, while the situation for the AGN sample Gaussian profile (i.e. 3σ away from the centre). NGC 3351 is a is more complicated. This is because there is non-stellar hot dust special case. Within the SINFONI FOV, the nuclear stellar light contamination in the near-infrared which causes dilution of the is entirely above the extrapolated bulge profile, and the integrated stellar features, making it challenging to extract the kinematics. luminosity is 32 per cent higher than expected. In addition, to match This issue will be discussed in Section 5.1. Looking at the stel- the radial profile of the excess, we included a second Gaussian to fit lar continuum maps, there are relatively noisy structures around the central cusp at a radius <0.5 arcsec, the slope of which is dis- the nuclear region in the AGN sample. This is because they are tinct from that of the 0.5–2 arcsec outermost regions. Interestingly, not direct measurements, but their K-band continuum includes the a similar situation in which there appear to be two components to non-stellar continuum from AGN and stellar continuum, the latter the nuclear stellar excess was reported for another nearby Seyfert 1 of which can be extracted via CO EW (note that ESO 137-34 and galaxy NGC 3227 by Davies et al. (2006, their figs 6 and 7). That NGC 5728 do not show any CO dilution and hence have no AGN work shows there is a clear excess starting at a radius of 0.5 arcsec hot dust observable in the K band). Overall, most galaxies (11/13) and the central cusp appears within a radius of 0.1 arcsec. In our in our sample show nearly symmetric stellar continuum maps with sample, NGC 3783 is a difficult case because the non-stellar con- regular elliptical isophotes. The two exceptions are NGC 7172 and tribution is strong across the whole SINFONI FOV. Thus, while we NGC 7582, for both of which the maps exhibit extreme irregulari- do measure an excess in the nuclear stellar luminosity, the scale is ties coinciding with known dust lanes (Bianchi et al. 2007;Smajic´ very uncertain and so we exclude it from our comparison of size et al. 2012). These pass across their nuclei and are clearly visible versus luminosity. Making use of the 10 objects with central excess in optical HST F606W images (Malkan, Gorjian & Tam 1998). It stellar light (see Table 2), we find the nuclear excess luminosity is is difficult to quantify the Ks-band extinction and correct it with proportional to the size of the excess component as shown in Fig. 7. present data. Fortunately, such an extinction does not have a ma- There is no significant difference in light excess between AGNs and jor influence on the extraction of stellar kinematics. Although the inactive galaxies. This size-luminosity relation can be written as stellar continuum asymmetry runs along the minor axis, there is no significant feature in the kinematics along the same direction. log(R ) = (0.52 ± 0.10) × log(L ) − (1.74 ± 0.73) (6) excess excess NGC 3783 suffers strong dilution from non-stellar light, making it We find that Spearman’s rank correlation coefficient is ρ ∼ 0.80 difficult to extract the kinematics and measure the PA. As a result indicating a 98 per cent significance for the correlation (noting that the kinematics maps for this AGN are very noisy. For galaxies NGC ρ = 1 corresponds to two variables being monotonically related). 6814 and NGC 4254 (Pair 8), the observed rotating velocity pattern A central stellar light excess has been found in different types is weak because they are both nearly face-on. This leads also to of galaxies and is usually considered to be a nuclear star cluster larger uncertainties in estimating the kinematic PA on small scales.

Figure 9. Simulation of the impact of non-stellar continuum contribution on CO EW and stellar kinematics from 100 synthetic spectra. Red lines are the median value at each CO EW bin, the red error bars represent the 1σ uncertainties. Left-hand panel: the fraction of non-stellar continuum as a function of CO EW. Middle panel: the velocity offset from the intrinsic stellar velocity measurement. Right-hand panel: the velocity dispersion ratio Figure 8. Radial averaged CO EW. Red filled circles and blue open circles of the simulation to the intrinsic measurement. Stellar velocity and velocity represent the AGN sample and the matched inactive galaxy sample. The dispersion start to deviate from the intrinsic measurements at CO EW ≤ decreased CO EW trends towards the centre in AGNs suggest the increasing 3–4 Å, suggesting any kinematic measurement below this CO EW range is contribution of non-stellar continuum. The FWHM radius of AO-corrected uncertain. PSF is 0.1 arcsec presented in black dashed line. been included in the synthetic spectrum to ensure that the S/N In the following sections, we discuss CO dilution and present the reaches ∼10 as the real data. The synthetic spectrum is then treated analysis of the 2D stellar kinematic maps. with the same analysis procedure as for the real data, measuring the kinematics and the CO EW. We repeat this process 100 times 5.1 Nuclear dilution by non-stellar light in order to make the experiment statistically robust. The results are illustrated in Fig. 9. The left-hand panel shows how much the For all the inactive galaxies, the stellar CO(2-0) EW has a relatively non-stellar continuum dilutes the CO EW. Once the CO EW be- uniform distribution. In contrast, most AGNs (6/8), with the ex- comes small, it is difficult to extract kinematics reliably because ception of ESO137-34 and NGC 5728, have a decreasing CO EW noise overwhelms the stellar absorption features. The middle and towards the centre. The reason for this is that the stellar absorption right-hand panel of Fig. 9 show the velocity offsets and the veloc- features are diluted by the strong non-stellar continuum which is ity dispersion ratios to the intrinsic stellar kinematic measurement. linked to hot dust associated with the AGN. Fig. 8 shows the ra- The velocity offsets and the velocity dispersion ratios deviate sig- dial CO EW gradient. The average intrinsic CO EW is 10–15 Å, nificantly when CO EW ≤ 3–4 Å. Below this CO EW threshold, the and for the inactive galaxies is slightly higher than typical value velocity offsets and the velocity dispersion ratios are dominated by of 11 Å reported by Burtscher et al. (2015), but within the range the randomly generated noise indicating that the CO EW threshold expected. We find there are four AGNs, for which the CO EW at is relatively sensitive to the data quality rather than just to the non- 1.5 arcsec is lower than the CO EW of inactive galaxies and other stellar continuum contribution fraction. Notably, NGC 7582 has a AGNs at the same radii. Their names are labelled in Fig. 8.For small CO EW in the centre but the velocity and velocity dispersion NGC 3783, NGC 4593 and NGC 7172, they have higher L14 − 195 can still be measured reliably even close to the AGN. The reason is and less obscuration with respect to other AGNs, suggesting, even that it is the brightest galaxy in our sample in the K band and the at 1.5 arcsec outer regions, the strong non-stellar continuum may noise in the data is small enough that we can extend the CO EW marginally dilute the stellar absorption features. We note here, in dilution limit to 2 Å. For other active galaxies, we are limited to a the case of NGC 3783 (the bright Seyfert nucleus in our sample), radius corresponding to a CO EW threshold of 3–4 Å, and exclude the CO bandhead appears to be very diluted everywhere within the any kinematic measurement within this radius. We have therefore 3 arcsec FOV. We therefore analyse also a SINFONI data cube with truncated this region in Figs 2–3. a FOV of 8 arcsec and find that the CO EW in outer regions is ∼8Å. We adopt this value as the intrinsic CO EW for this galaxy, despite it being lower than the mean value we found in the other galaxies. 5.2 Kinematic PA versus photometric PA In contrast, there is no CO dilution in ESO 137-34, and the CO EW In this section we compare the PA from the fits to the small of ∼10 Å across the whole FOV is likely to be intrinsic, implying scale kinematics (PAkin) with the large scale photometric data the age of stars could be different from those galaxies with CO EW (PAphoto). The kinematic PA is derived from the SINFONI stellar of 12–15Å (Davies et al. 2007). For the purpose of assessing the velocity map using the software developed by the SAURON team impact of the non-stellar continuum on the kinematics extraction, (Cappellari et al. 2007;Krajnovicetal.´ 2011)3. The kinematic PA we produce a simple test to simulate the observed CO EW dilution. is listed in Table 2. We obtain the photometric PA from the cata- We start with the best-fitting template spectrum of NGC 7727 (an logue for the Spitzer Survey of Stellar Structure in Galaxies (S4G), inactive galaxy without any non-stellar contamination) and add a which observed numerous nearby galaxies at 3.6 and 4.5 μmwith pure blackbody emitter with temperature of 1000 K, representing the Infrared Array Camera (IRAC). This catalogue has the advan- the non-stellar continuum (Riffel et al. 2009; Burtscher et al. 2015) tages that the seeing has been excluded when fitting the photometric ellipses and the observations cover the extension of the large scale Fsynthetic = (Ftemplate × (1 − c)) + (Fblackbody × c)(7) where c is the fraction of blackbody emitter, increasing from 0 per cent to 100 per cent, in the steps of 10 per cent: noise has 3 http://www-astro.physics.ox.ac.uk/∼mxc/software/

throughout this paper have been corrected for inclination based on the large-scale host galaxy inclination, which is listed in Table 1. The approximate dynamics of a stellar system can be established by the velocity and velocity dispersion, which reflect the contributions of rotation and random motion. The relative contribution between these two motions is written as v/σ and indicates how discy or spheroidal the system is. To access the enclosed√ dynamical mass in the nuclear region, we use the quantity v2 + σ 2. The radius over which we can compare AGNs and inactive galaxies is in the range of 20–150 pc: most AGNs are affected by non-stellar dilution meaning the kinematic information cannot be extracted from the Figure 10. Left-hand panel: the Spitzer photometric PA plotted against the inner 20 pc, and most inactive galaxies are so close to us that the SINFONI kinematic PA. The photometric PA is redrawn from S4G cata- FOV does not extend over regions beyond 150 pc. logue. The kinematic PA is measured by SINFONI stellar velocity field (see In Fig. 11, we find that all the quantities are comparable between the third rows in Figs 2–4). The black dotted line is the 1:1 relation. Right- AGNs and inactive galaxies across 20–150 pc, suggesting that the hand panel: histogram showing the distribution of PA difference measured nuclear stellar kinematics of the AGN sample are similar to those of with two independent methods. the matched inactive galaxy sample. In an examination of the eight individual pairs, no specific trend towards the AGN or inactive disc. NGC 3783 has been excluded in our comparison because there galaxy sample is shown by any of the stellar kinematic quantities. is no PA measurement from the catalogue, which may be due photo In contrast, within a radius of 200 pc Hicks et al. (2013) found a to its bright Seyfert 1.5 nucleus preventing a measurement. Fig. 10 √ large difference in σ and a smaller difference in v2 + σ 2, both of shows that the PAkin is in good agreement with PAphoto, the differ- ◦ ◦ these quantities being smaller in the AGN sample compared to their ences between two measurements being in the range 8 ± 6 .Inthe inactive sample. The authors interpreted this to indicate there is a following study, we simply adopt the mean of these two PAs and ◦ dynamically cold nuclear structure composed of a relatively young set ±5 as the uncertainty. For comparison, the difference between stellar population in the AGN sample. our PA and PA is a factor two larger than Barnes & Sellwood kin photo There could be several reasons for these differing results. (2003) found, but it is robust enough for our analysis presented be- One possibility is the AGN selection method: we use solely the low. A similar result has been found in 16 nearby Seyferts with using 14–195 keV luminosity to select AGN while Hicks et al. (2013) Gemini NIFS data, both the large-scale photometric and small-scale used Seyfert galaxies that meet the Revised Shapely–Ames (RSA) kinematic axis are well aligned (Riffel et al. 2017 submitted). We catalogue magnitude requirement (B < 13.4 mag). It is worth noting note that NGC 4254 has the largest uncertainty when calculating also that log L − of the AGNs in our sample is 43.0 ± 0.4, which the kinematic PA and NGC 6814 has the largest inconsistency in 14 195 is a factor of a few brighter than those in the Hicks et al. (2013) the measurements. It is because they are both face-on galaxies. sample where log L14 − 195 is 42.4 ± 0.4 (and there is one AGN without a Swift-BAT detection). A second possibility is the limited 5.3 Radial average kinematics sample size and the selection variation. In this study we use eight AGNs and five inactive galaxies while Hicks et al. (2013)usedfive We use the IDL routine kinemetry to extract radial distributions for the AGNs and four inactive galaxies in their kinematic comparison. As velocity and velocity dispersion from the 2D kinematic maps. The such, simple scatter in the individual properties at small scales could details of the method are described by Krajnovic´ et al. (2006). Here lead to the discrepancy. If all the objects in the LLAMA sample are we briefly summarize the key equations, which provide an important observed, we will be able to resolve this issue. A third possibility insight to quantify the physical meaning. By using Fourier analysis is the selection of the matched inactive galaxies. In both cases, this to characterize the periodicity, the observed kinematic moments was done on parameters including galaxy integrated luminosity, can be divided into a series of elliptical rings, each of which can be Hubble type, inclination, bar and distance. However, a difference written as a finite sum of harmonic terms is that we selected based on H-band luminosity, while Hicks et al. N (2013) used matched samples from Martini et al. (2003)thathad K a,ψ = A a + A a nψ + B a nψ ( ) 0( ) n( ) sin( ) n( )cos( )(8)been selected on B-band luminosity. Due to the reduced impact of n=1 extinction and stellar age on the luminosity in the near-infrared, where ψ is the azimuthal angle measured from the projected major the H band is a more reliable proxy for stellar mass. Hicks et al. axis in the plane of the galaxy, and a is the length of semimajor axis (2013) discussed this issue and found that the H-band luminosity of the elliptical ring. The parametersAn and Bn can be represented for their AGN was 24 per cent less than in their inactive sample. 2 2 by the amplitude coefficient Kn = (An + Bn ). With respect to If H-band luminosity does linearly trace mass as we expect, this the shape of elliptical rings for our analysis, the PA is set to be the could then lead to a ∼12 per cent difference√ in kinematic tracers. mean PA obtained in Section 5.2, the flattening (q) is the axial ratio This would reduce the difference in v2 + σ 2 to a level where it listed in Table 1 and the central position is fixed at the location given is insignificant, but could not account for all the difference in σ . by the centre of the brightest continuum. For an ideal rotating disc, Nevertheless, it underlines the importance of careful matching of the rotational velocity and velocity dispersion fields are dominated the control sample. by K1 and A0. The rotational velocity has been corrected for the inclination listed in Table 1. 5.4 Central velocity dispersion For the purpose here, to study the differences in stellar properties between AGNs and inactive galaxies, we plot in Fig. 11 four When looking at the nuclear stellar kinematics, some AGNs show quantities related to the stellar kinematics√ as a function of radius: a significant velocity dispersion drop, suggesting the presence of a velocity, velocity dispersion, v/σ and v2 + σ 2. The velocities used dynamically cold nuclear component (Emsellem et al. 2001; Greene

Figure 11. Radial average kinematic properties of the CO(2-0) stellar absorption: AGNs and inactive galaxies are represented in pink and navy blue points. The mean value (uniformly weighted) of AGN and inactive galaxy sample are illustrated as bold red and blue lines, respectively. Beyond 150 pc, there is only one inactive galaxy NGC 4224 that has measurements, other inactive galaxies being so close that their outer regions exceed our SINFONI FOV. On the other hand, below 20 pc, there is only two AGNs, ESO 137-34 and NGC 5728, that have measurements, others have non-stellar continuum that prevent us to extract the stellar kinematics. The typical error bars of the lines are the standard deviation at that radius and the radial bin size. We show√ the stellar kinematic properties with four quantities: inclination-corrected rotational velocity (top left), velocity dispersion (top right), v/σ (bottom left) and v2 + σ 2 (bottom right). The velocities have been corrected for inclination based on the large-scale host galaxy inclination, which is listed in Table 1.

et al. 2014). Self-consistent N-body simulations interpret these stel- In contrast to the case of NGC 3351, looking at the overall re- lar velocity dispersion drops in the nuclear region as a consequence sults of our sample, we surprisingly find that the excess stellar of young stars born from the dynamically cold gas reservoir com- light is not generally accompanied by the drop of stellar velocity ing in from larger scales. As such, nuclear disc formation requires dispersion towards the centre. These phenomena do not appear to in situ star formation, and it is kinematically cooler than the sur- correlate with each other, and the stellar velocity dispersion across roundings (Cole et al. 2014). The simulations further suggest the the observable FOV is generally rather uniform. This observational young stellar population (less than 0.9 Gyr) should be brighter evidence is quite distinct from the Wozniak et al. (2003) simula- than the old underlying population at near-infrared wavelengths tions, figs 9 and 10 of their paper present that the stellar velocity (Wozniak et al. 2003). Adaptive optics observations with SINFONI dispersion drops with the increasing contribution of young (dynam- have shown two AGNs where this is seen (NGC 1097 and NGC ically cold) stellar population. Once the mass density of the young 1068, Davies et al. 2007). And our new SINFONI observations can population significantly overtakes the old population, the drops of be used to test this interpretation further, as well as to assess whether stellar velocity dispersion can be easily seen. Looking at our data, a young stellar population commonly occurs in AGNs. the reason why we do not see the clear velocity dispersion drops The nuclear stellar light excesses we have discussed in Section 4 in the central hundred pc scales, is probably because the contribu- exhibit an extended structure and a velocity field that indicates ro- tion of old stars dominates over the young stars. To test this sce- tation, suggesting that they are nuclear discs. In particular, our data nario, we describe a simple toy model to interpret the LOS velocity for the inactive galaxy NGC 3351 are consistent with the above dispersion. mentioned simulations: it exhibits significant excess stellar light Based on the hydrodynamical disc models, σ los (line-of-sight across the whole FOV, which is accompanied by an obvious central velocity dispersion) can be projected into σ R (azimuthally aver- −1 velocity dispersion drop to about ∼50 km s . We can compare this age radial dispersion), σ θ (tangential average radial dispersion) and to recent hydrodynamic simulations of the evolution of star forma- σ z (vertical average radial dispersion) in cylindrical coordinates. tion as a result of gravitational instabilities in a nuclear gas disc The σ R and σ θ are parallel to the disc plane, their contribution (Schartmann et al. MNRAS accepted). These show that, because of is marginal when the disc close to face-on [inclination ∼0◦,i.e. the large number of interactions between gas clumps and as a result the angle between line of sight and the disc is 90◦; see equations of scattering between stars and gas clumps, the stellar disc under- (28) and (29), and figs (7) and (8) in Tempel & Tenjes 2006]. For goes significant gravitational heating before it relaxes in the global simplicity, we assume that the simple toy models are all close to σ 2 ∼σ 2 potential of the bulge. These authors show that in their simulation, face-on. Then los can be seen as z , in which the vertical velocity −1 the velocity dispersion can attain a constant value of ∼40 km s . dispersion (σ z(r)) can be derived from the surface density (r)in

the disc: 2 σz (r) = 2πG(r)hz (9)

where hz is the scale-height of the disc. Although this may vary with radius, we assume the disc models have a constant hz because in Section 3.2, we find that the bulges in our galaxies typically have nbulge ∼ 2, and hence are likely to be pseudo- bulges instead of classical bulges with n = 4. The bulge decomposition provides the bulge surface density profile which allows us to calculate the intrinsic velocity dispersion of bulge (σ bulge). In addition, we set a second velocity dispersion (σ new) to represent the young stellar population with a lower velocity dispersion of 40–50 km s−1. Adopting equation (1) from Wozniak et al. (2003), the line-of-sight velocity dispersion pre- dicted by the toy model is weighted by the luminosity of two components (i.e. bulge and nuclear excess). It can be expressed as L (r) σ 2 (r) = σ 2 (r) × bulge los,mod z,bulge L (r) total L (r) + σ 2 r − bulge z,new( ) 1 (10) Ltotal(r) We apply this toy model to all objects and find that in its simplest form above, it can already explain the observed trend of velocity dispersion for NGC 7213 (AGN), which is presented Fig. 12. This galaxy has strong nuclear excess stellar luminosity. By check- ing its galactic plane inclination, we find NGC 7213 is close to face-on (26◦), which is consistent with one of the assumptions in our simple toy model. Inspection of Fig. 12 shows that the bulge contribution still dominates within the whole FOV, with the result that the kinematic signature of the young stars is dominated Figure 12. The best sample of simple toy model to explain the trend of radial by that of the old stars, and hence the lower velocity dispersion stellar velocity dispersion. Top panel: the radial luminosity for observed from the young population is hidden by the dynamically hot galac- data point (black pluses) and bulge component (red dashed line). Middle tic bulge. The increase in velocity dispersion at smaller radii is panel: the bulge fraction as a function of radius. Bottom panel: the radial reduced, but not enough to be manifested as a drop in velocity stellar velocity dispersion with radius. The black solid line represents the dispersion. Thus we can argue that we would not expect to see a intrinsic bulge velocity dispersion, which is calculated based on the bulge clear stellar velocity dispersion drop in the centre. But, because surface brightness profile. Considering the contributions come from both a −1 we do not know the true intrinsic radial dispersion profile of the dynamically hot bulge population (typical is several hundred km s )and −1 (pseudo-)bulge, we also cannot claim that the excess stellar lumi- a dynamically cold young star population (we assume 40–50 km s ), the luminosity-weighted velocity dispersion is presented in blue dashed line. nosity must be associated with a dynamically cooler stellar popula- Pink pluses are the observed data with the error bar representing the 1σ tion. error with respect to the velocity dispersion inside the 2D elliptical rings at There is another explanation that most of the stars embedded in specific radius. We attached the PPXF return mean stellar velocity dispersion nuclear disc have not formed recently, and this stellar component is error (25 km s−1 in average) in the bottom left corner. not dynamically cold anymore. Sarzi et al. (2016) find that the age of hot nuclear stellar disc in elliptical galaxy NGC 4458 is at least 6 activity on and off, especially X-ray activity, is shorter than the Gyr old, while Corsini et al. (2016) measured the age of the nuclear time-scale to form nuclear stars. On the other hand, focusing on stellar disc in the SB0 galaxy NGC 1023 is about 2 Gyr. On the other individual galaxies, we find that NGC 3351 has two components of hand, spectral synthesis fits to the detailed XSHOOTER spectra nuclear stellar excess, together with a significant velocity dispersion of the LLAMA sample (Burtscher et al. in preparation) show that drop towards the centre, indicating recent star formation around the while an old population dominates the optical continuum, a younger galactic nucleus. These properties are similar to those reported in component with an age of 0.1–1 Gyr is nearly always present at a previous studies about recent star formation around AGN in Seyfert level of a few to 20 per cent. galaxies (e.g. NGC 3227 in Davies et al. 2006). It implies that, In addition to the question of whether the young stellar popula- although there may be indications of gas inflow which triggers star tion is dynamically cold, a second issue concerns whether there is formation and then feeds the AGN, there could still be a discrep- a difference between active and inactive galaxies. In this study, we ancy between the time-scales of these phenomena, with the AGN find there is no significant difference in stellar surface brightness switching on and off multiple times during the period in which the and stellar kinematics between AGNs and most inactive galaxies; nuclear stars can still be seen. although we note that there are two inactive galaxies with surface brightness substantially lower than the rest of the sample. Similarly 6 CONCLUSIONS photometric and kinematic characteristics between AGN and inactive galaxies suggest that the nuclear stellar properties are generally We present SINFONI data for the first half of a complete vol- comparable. This suggests that the time-scale of switching AGN ume limited sample of bright local Seyferts, selected from the

14–195 keV Swift-BAT catalogue. These AGNs have been assigned tific and Technological Development (CNPq) for financial support. a matched sample of inactive galaxies, in which the host galaxy MK acknowledges support from the Swiss National Science Foun- properties (stellar mass, Hubble type, inclination, presence of a bar) dation (SNSF) through the Ambizione fellowship grant PZ00P2 share a similar distribution. In this paper, we present an analysis of 154799/1. R.R. thanks CNPq and Fundaçao˜ de Amparo a` Pesquisa the spatially resolved stellar luminosity and kinematics for a sample do Estado do Rio Grande do Sul (FAPERGS) for financial support. of eight pairs of matched active and inactive galaxies, covering their This research is based on observations collected at the European Or- central few hundred parsecs. Observations on this scale enable us to ganization for Astronomical Research in the Southern hemisphere approach the galactic nucleus and search for a young stellar popula- under ESO programmes: 093.B–0057(A) & 093.B–0057(B). It also tion, which simulations suggest, should be brighter at near-infrared makes use of data products from 2MASS, which is a joint project wavelengths and dynamically colder than the old population in the of the University of Massachusetts and the Infrared Processing and large-scale bulge. Based on this small set of galaxies, the main Analysis Center/California Institute of Technology funded by the findings from the kinematic and photometric perspectives are given National Aeronautics and Space Administration and the National below. Science Foundation. 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Table A1. (1) Galaxy name, upper rows are AGNs and lower rows are inactive galaxies; (2) Bulge Sersic´ index; (3) Bulge effective radius; (4) Bulge position angle; (5) Bulge axis ratio; (6) Bulge to total ratio; (7) Disc effective radius; (8) Disc position angle; (9) Disc axis ratio; (10) Bar Sersic´ index; (11) Bar effective radius; (12) Bar position angle; and (13) Bar axis ratio.

(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) Galaxy name nbulge r e; bulge PAbulge bulge B/T r e;disc PAdisc disc nbar r e;bar PAbar bar (arcsec) (◦) (arcsec) (◦) (arcsec) (◦)

ESO 137-34 2.13 6.94 −45.0 0.75 0.22 27.15 [35.0] 0.91 0.31 8.02 [−16.0] [0.3] NGC 3783a 1.24 1.45 [−20.0] 0.95 0.21 19.53 −21.0 0.80 0.5 12.27 [−20.0] 0.26 NGC 4593 (2MASS) 2.73 3.66 −85.0 0.83 0.41 38.64 71.0 0.57 [0.5] 37.65 55.0 0.29 NGC 4594 (HST) 1.67 8.1 [−85.0] 0.80 – – – – – – – – NGC 5728 1.1 4.02 3.7 0.92 0.23 48.85 32.0 0.37 [0.5] 42.5 34.0 [0.1] NGC 6814 1.08 1.07 27.0 0.94 0.09 30.53 56.0 0.96 [0.5] 5.43 26.0 0.66 NGC 7172 1.16 3.55 −89.0 0.64 0.25 27.21 −84.00.50–– – – NGC 7213 2.57 13.7 −16.0 0.96 0.7 39.72 80.0 0.86 – – – – NGC 7582 2.72 1.99 −35.0 0.68 0.28 50.21 −25.0 0.38 0.27 54.71 [−22.0] [0.15] NGC 718 1.32 2.09 −5.0 0.92 0.28 16.25 0.0 1.0 0.73 15.73 −27.0 0.42 NGC 3351 0.8 6.95 12.0 0.77 0.22 61.64 0.0 0.89 [0.5] 38.42 [−70.0] 0.3 NGC 4224 2.53 5.01 [55.0] 0.72 0.29 28.42 [55.0] 0.43 – – – – NGC 4254 1.99 12.79 65.0 0.74 0.19 41.44 69.0 0.88 – – – – NGC 7727 1.68 5.07 −80.0 0.72 0.36 22.86 10.0 0.95 [0.5] 12.73 [−90.0] 0.15 Note. aAdding PSF to take into account the central bright nucleus. Brackets: We hold the components ﬁxed to the values in order to optimally perform galaxy ﬁtting.

APPENDIX B: RADIAL FLUX AND KINEMATICS OF EACH GALAXY We show the radial ﬂux along the major-axis PA (top and middle rows) and the average kinematics (bottom row) for each galaxy.

Figure B1. ESO 137-34 (Active galaxy in Pair 1). Top left panel: the radial flux profile along the major axis of 2MASS Ks-band image (black asterisk signs). The decomposed disc, bar and bulge component are presented in blue dashed line, green dashed line, and red dashed line, respectively. The yellow solid line indicates the integrated radial flux profile. This plot together with 2MASS radial residual enables us to identify the non-fitted structures (e.g. spiral arms). The horizontal black dotted line represents a residual value equal to zero. Top right panel: the combined radial flux profiles along the major axis from the large scale 2MASS Ks image (black asterisk signs; at a radius ≥ 2 arcsec) and small scale SINFONI stellar continuum image (black plus signs; at a radius ≤ 1.5 arcsec). The HST F160W radial flux profile (orange plus signs) is added to reinforce the scaling factor between two different scales. The red dashed line represents the bulge Sersic´ profile. The vertical black dotted line is the SINFONI AO mode PSF, FWHM radius of ∼0.1 arcsec. This plot together with SINFONI (and HST) radial residual enables us to identify whether there is an excess towards the centre. The horizontal black dotted line represents a residual value equal to zero. Middle left panel: the radial flux profile of SINFONI stellar lights (black plus signs). The red dashed line indicates the inward extrapolation of the fitted bulge Sersic´ profile to SINFONI FOV. The dashed line encloses the extended radius of nuclear stellar excess component. Middle right panel: the radial flux profile of nuclear stellar excess (the inward extrapolation of the fitted bulge Sersic´ profile has been subtracted) and fit a simple Gaussian profile that is plotted as a purple solid line. Bottom left panel: the circular velocity of stars as a function of radius to the SINFONI FOV, which is extracted by using the IDL routine kinemetry. The inclination has been corrected based on the large-scale host galaxy inclination. Black dashed line is the size of nuclear excess component. Bottom right panel: the LOS velocity dispersion of stars as a function of radius to the SINFONI FOV, which is extracted by using the IDL routine kinemetry. Black dashed line is the size of nuclear excess component. Pink solid line is the mean LOS stellar velocity dispersion at the radius larger than black dashed line, pink dashed lines are the ±3σ errors of mean LOS stellar velocity dispersion, which can be a criterion to check whether there is a significant variation in the centre [refer to column (5) in Table 2].

Figure B2. NGC 718 (Inactive galaxy in Pair 6). See Fig. B1 for similar descriptions.

Figure B3. NGC 3351 (Inactive galaxy in Pair 7). The excess ﬂux distributes entire SINFONI FOV, the black dashed lines in the middle and bottom rows present the size of nuclear cusp. Furthermore, the velocity dispersion drops can be obviously seen inside the nuclear cusp. Other similar descriptions can be seen in Fig. B1.

Figure B4. NGC 3783 (Active galaxy in Pair 6). Because its nucleus is bright in 2MASS Ks image, we add additional PSF during 2D ﬁtting and plot it as deep pink dashed line in the top left panel. Other similar descriptions can be seen in Fig. B1.

Figure B5. NGC 4224 (Inactive galaxy in Pair 3 and Pair 5). See Fig. B1 for similar descriptions.

Figure B6. NGC 4254 (Inactive galaxy in Pair 8). See Fig. B1 for similar descriptions.

Figure B7. NGC 4593 (Active galaxy in Pair 7). Top left panel: in addition to measure bulge Sersic´ profile based on 2MASS image, we use GALFIT to fit HST F160W image, which is presented in red dot–dashed line. Top right panel: the combined large-scale 2MASS, HST images and small-scale SINFONI image. We do not see any significant nuclear stellar excess towards the centre in both 2MASS and HST residuals. Middle and bottom panels: see Fig. B1 for similar descriptions.

Figure B8. NGC 5728 (Active galaxy in Pair 4). See Fig. B1 for similar descriptions.

Figure B9. NGC 6814 (Active galaxy in Pair 8). See Fig. B1 for similar descriptions.

Figure B10. NGC 7172 (Active galaxy in Pair 3). See Fig. B1 for similar descriptions.

Figure B11. NGC 7213 (Active galaxy in Pair 2). See Fig. B1 for similar descriptions.

Figure B12. NGC 7582 (Active galaxy in Pair 5). See Fig. B1 for similar descriptions.

Figure B13. NGC 7727 (Inactive galaxy in Pair 1, 2 and 4). See Fig. B1 for similar descriptions.

This paper has been typeset from a TEX/LATEX ﬁle prepared by the author.

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